This invention relates to a tire pressure control device used on a motor vehicle, and particularly to an apparatus for mounting the electronic emitter component of the tire pressure control device so that the electronic emitter is insulated from the high temperatures occurring in the mounting area.
Known devices for the control of the tire pressure of a motor vehicle include a manometric switch that is fastened to the rim of the motor vehicle and rotates with the wheel as well as an electric emitter attached to the axle which does not rotate. The emitter is disposed in the rim dish in the space between the brake disk and the base of the rim and is therefore exposed to relatively high temperatures caused by the adjacent brake disk and caliper. Temperatures of over 750.degree. C. occur at the brake disk and because of radiative transmission of the heat, this results in temperatures at the emitter of about 250.degree. C. During the cooling phase of the brake disk, the caliper temperature increases so that during a short period of time, the temperature of 250.degree. C. remains constant and no significant cooling occurs. These relatively high temperatures can destroy the electronic part of the emitter or can cause an erroneous signal which leads to incorrect operation of the tire pressure control device.
The object of the present invention is to provide a tire pressure control device which is able to operate properly despite the relatively high ambient temperatures.
According to the present invention, the electronic emitter component of a tire pressure control device is mounted on the caliper portion of the brake assembly in such a manner that the emitter is insulated from the high ambient temperatures occurring in the mounting area.
The main advantages achieved by the present invention are that the heat-sensitive part of the emitter is shielded from the relatively high ambient temperatures by a housing and thus the emitter is exposed to only those temperature-caused stresses that do not have a negative effect on its operation.
By using a high-temperature-resistant and high-strength plastic, such as polyimide, which also exhibits low thermal conductivity, the design of the housing can be thin-walled. As a result, only a small space is required at the mounting site between the brake disk and the base of the rim, this space being limited since the manometric switch projects into this space and an air gap must exist between the emitter and the manometric switch.
By using a heat-insulating material on the side of the emitter facing the brake disk, a temperature of 100.degree. C. can be maintained on the bottom side of the emitter even when the temperatures of the brake disk reach 880.degree. C. By using a housing made of a plastic material having low thermal conductivity in combination with a material with high heat-insulating capabilities, an optimal shielding against heat is achieved which ensures high operability and a long useful life.
In order to limit the introduction of heat into the emitter to as low a level as possible, the housing is connected with a holding means attached to the axle via a clamping means which, as compared to a fixed screw-type connection, has the advantage of transmitting less heat to the emitter. In the case of conventional screw connections between the holding means and the housing, the housing would be subjected to a melting effect and thus the emitter would be subjected to higher temperatures than in the present invention.
The only screw-type connection between the holding means and the housing is arranged in a fastening part in such a way that it is sufficiently removed from the sensitive parts of the electronic emitter so that the heat transmitted by the screw does not harm the emitter. By using a detachable fastening part, it is possible to remove the housing and exchange the emitter in a simple manner. Also, by removing a cover, the encapsulated insulating material can be replaced. The cover is secured in a watertight manner preferably by the use of a silicone material to prevent the insulating material from absorbing moisture since this would considerably decrease its heat-insulating characteristics.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purpose of illustration only, an embodiment in accordance with the present invention.